A new study of the health of highly impacted coral reefs off Singapore over a 27-year period has shown they are more resilient to the effects of human activity and sea warming than previously thought.
University of Nottingham coral reef scientist Dr David Feary was part of an international team that found that shallow coral reefs rebounded rapidly from a major bleaching episode in 1998, despite experiencing such high levels of sedimentation that underwater visibility was typically less than two metres.
Dr Feary, from the University's School of Life Sciences, said: “Although this region has had its fair share of impacts, our work is now shining a light on the potential resilience of coral reefs to a range of human and climate mediated factors. We believe this research now offers a window into determining the mechanisms which may provide new hope for reef conservation globally.”
Dr James Guest, from the Hawai’i Institute of Marine Biology, said: “It is remarkable that diverse shallow coral communities can persist in such adverse conditions. Undoubtedly, Singapore’s reefs have suffered as a result of human activities, but the recovery of corals at shallow sites is really surprising given how impacted this environment is. It really shows how tough corals can be.”
In the past 200 years, Singapore has been transformed from a forest-covered island with a population of 150 people to a highly urbanised city-state of more than 5.4 million.
Extensive coastal construction, dredge spillage and land reclamation have resulted in coastal waters being impacted by high sedimentation rates, turbidity and pollution, putting immense pressure on the surrounding coral reefs.
Between 1986 and 2012, coral communities at 15 sites on the southern side of Singapore island were regularly surveyed, and the results have been analysed for the new study.
Coral cover during this 27-year period declined at all sites — by about 12 per cent at the shallower depths of 3-4 metres and by about 30 per cent at the deeper depths of 6-7 metres. There was a particularly large decline in the first decade due in part, the authors suggest, to unmitigated dumping of dredge spoils in the late 1980s.
In 1998, a major bleaching event occurred as the result of high water temperatures associated with an El Nino. However, corals at shallower reef sites were remarkably resilient to this event, showing signs of recovery within a decade. By 2008 coral cover had increased to about 1993 levels.
University of New South Wales Professor Peter Steinberg, lead researcher on the project, said: “This is by no means a cause for complacency regarding the state of our reefs, but rather highlights that if we can reduce local stressors, reefs are more likely to be able to rebound from the effects of global stressors such as climate change.”
Corals at deeper sites were less resilient, with coral cover at these sites continuing to decline. However, none of the sites were overtaken by large fleshy seaweeds, as has been seen on impacted reefs elsewhere in the world. The lack of recovery at deeper sites may be due to low light levels or a lack of unsuitable substratum for new corals to settle and survive.
The researchers suspect the resilience at shallow sites is due to an abundance of coral species which have fast regrowth rates and can tolerate environmental stresses such as high levels of suspended sediments. It is also possible the turbidity of the water could offer some protection by reducing the light and the impact of heat stress, as well as slowing down the growth of fleshy seaweeds.
The study by the team, which includes researchers from University of New South Wales and the Sydney Institute of Marine Science, the National University of Singapore, Nanyang Technological University and Singapore’s National Parks Board, is published in the journal Scientific Reports.
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Notes to editors: The University of Nottingham has 43,000 students and is ‘the nearest Britain has to a truly global university, with a “distinct” approach to internationalisation, which rests on those full-scale campuses in China and Malaysia, as well as a large presence in its home city.’ (Times Good University Guide 2016). It is also one of the most popular universities in the UK among graduate employers and was named University of the Year for Graduate Employment in the 2017 The Times and The Sunday Times Good University Guide. It is ranked in the world’s top 75 by the QS World University Rankings 2015/16, and 8th in the UK for research power according to the Research Excellence Framework 2014. It has been voted the world’s greenest campus for four years running, according to Greenmetrics Ranking of World Universities.
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